The invention relates to a seat adjuster, comprising a brake which acts between a fixed part and an adjustable part and by means of which the adjustable part can be blocked in different positions on the fixed part, and which can be released by means of a release element, an adjustment element, which acts on the release element, for selectively adjusting the adjustable part in two opposite directions, and a locking element, which automatically engages and interlockingly locks the adjustable part to the fixed part when the adjustment element is not actuated, and automatically disengages when the adjustment element is actuated, wherein the disengagement of the locking element and the adjustment of the adjustable part can be effected by moving the adjustment element out of a neutral position in one of the two directions.
EP 0 979 179 B2 describes a seat adjuster of this type which may for example serve for adjusting an inclination of a seat back or a height adjustment of a vehicle seat. The fixed part is rigidly mounted on the vehicle seat or the vehicle body, whereas the adjustable part effects the desired adjustment of the vehicle seat. The adjustment element has a lever which can be pivoted from a neutral position in two opposite directions in order to adjust the seat either in the one direction or the other direction. By repeated “pumping” with the adjustment element, it is possible to adjust the vehicle seat step-wise over a larger adjustment range. When the adjustment element is displaced from the neutral position, the brake entrains the adjustable part. When the user releases the adjustment element, the adjustable part is locked by the brake in the position reached at that time, whereas the adjustment element is returned to the neutral position under the action of a return spring, so that another adjustment stroke can be performed if necessary.
The brake is preferably formed by a so-called freewheel brake wherein the blocking of the adjustable part on the fixed part is effected by clamp rollers and associated clamp contours. This has the advantage that a practically continuous adjustment is possible, and—other than in case of a ratchet mechanism, for example—disturbing noises are hardly produced. If, however, the adjustable part is subject to a permanently acting torque over a longer period of time, for example, in case of a seat height adjuster, due to the proper weight of the vehicle seat or the weight of a person sitting thereon, vibrations that occur when the vehicle is in motion may lead to a gradual roll-off of the clamp rollers at the races of the brake and, therewith, to an undesired gradual adjustment of the vehicle seat. In the known seat adjuster, this effect is avoided by additionally locking the adjustable part on the fixed part with interlocking engagement.
In the known seat adjuster, the locking element is formed by pivotable pawls, which, in the locked position, engage a gear ring that is rigidly coupled to the adjustable part and, in an initial phase of an adjustment operation, is tilted out of the locked position. Due to this construction, the locking element can withstand only a limited torque.
For safety reasons, seat adjusters for vehicles have to be designed such that they safely hold the seat in the adjusted position even when, in case of an accident, an extremely high torque acts upon the seat adjuster due to forces of inertia that are generated in an impact. For this reason, the freewheel brake of the known seat adjuster is designed such that the adjustable part is safely locked on the fixed part even in case of a very high torque.